Image forming system

ABSTRACT

A sheet position detecting portion which detects a position of the sheet in which the image is formed by the image forming portion, a control portion which controls a motion of the inverting portion, and a sheet post-processing apparatus which is connected to the image forming portion and receives the sheet discharged from the discharging portion so as to apply an post-processing, and the control portion can change the motion of the inverting portion based on a detected information of the sheet position detecting portion, in such a manner that an interval time of the continuous sheets becomes equal to or more than a sheet interval time which the sheet post-processing apparatus can receive the sheet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming system in which asheet post-processing apparatus can be connected to an image formingportion.

2. Description of the Related Art

Generally, in the image forming system, in order to enhance aproductivity, a subsequent sheet is sequentially fed without waiting foran image formation of a preceding sheet. Accordingly, a plurality ofsheets exist in a conveying path. Further, if the preceding sheet isretarded, the subsequent sheet is temporarily stopped following thepreceding sheet, in such a manner as to prevent the subsequent sheetfrom catching up on the preceding sheet.

Conventionally, in this kind of image forming system, an inverseconveying unit is driven at a constant speed or timing, a conveyingspeed and a conveying timing of a recording sheet are changed by achange of a conveying performance, and a dispersion is generated in apaper interval so as to be an obstacle in the case of increasing acontinuous image forming efficiency. In other words, it is necessary toset a paper interval wide for avoiding a conveying failure due to thedispersion of the paper interval. As a result, it is hard to enhance theimage forming efficiency.

In order to solve the problem mentioned above, there is an image formingapparatus structured such that a continuous image is formed always at aconstant paper interval, by carrying out a conveying control correctinga change of a conveying performance of an inverse conveying unit whichtends to be affected by a change such as an abrasion based on anactuation for a long term (refer to Japanese Patent ApplicationLaid-Open No. 2002-211815).

Further, there is an image forming apparatus structured such that aconveying failure is prevented by defining a distance interval betweensheets constant and inverting the sheet, in accordance with a speedingup of the image forming apparatus (refer to Japanese Patent ApplicationLaid-Open No. 2001-240285).

In these image forming apparatuses, it is not necessary to take intoconsideration a dispersion at a time of setting the paper interval inthe continuous image forming, it is possible to narrow down the paperinterval, and it is possible to enhance the productivity of the imageforming apparatus.

Further, in the conventional sheet post-processing apparatus, since thepaper interval time which can execute the post-processing is narrowerthan the paper interval time of the image forming apparatus so as toafford, the post-processing can be executed without degrading theproductivity, even if the paper interval dispersion exists within theimage forming apparatus. Japanese Patent Application Laid-Open No.2002-311659 sets the sheet interval to which the post-processingapparatus can correspond. The sheet interval set in the structure ofJapanese Patent Application Laid-Open No. 2002-311659 is set whilehaving a margin such that the post-processing apparatus can correspondeven if a slip between the sheet and the conveying roller is generatedwithin the image forming apparatus. Accordingly, there is a limit forshortening the interval between the sheets within the image formingapparatus so as to improve the productivity.

In this case, in an accessory (ACC) such as the sheet post-processingapparatus receiving the image forming apparatus having a highproductivity in an in-line, the paper interval time which can executethe post-processing becomes approximately equal to the paper intervaltime of the image forming apparatus.

Accordingly, if the paper interval of the image forming apparatusbecomes shorter than the paper interval time which the sheetpost-processing apparatus can execute the post-processing, at a timewhen the paper interval is dispersed in the image forming apparatus,whereby the sheet is discharged from the image forming apparatus so asto be sent to the post-processing apparatus, there is a risk that thepaper interval can not be corresponded by the sheet post-processingapparatus.

In the conventional paper interval dispersion suppressing unit (refer toJapanese Patent Application Laid-Open No. 2002-211815), a driving unitof an inverse conveying unit is controlled in such a manner as to detecta change of a conveying performance of the inverse conveying unit andachieve a constant conveying performance based on the detection,however, it does not take into consideration a paper interval between apreceding paper under conveying and a subsequent paper.

Accordingly, in the case that the paper interval changes suddenly, thepaper is discharged from the image forming apparatus as it is withouttaking into consideration a receiving condition of the post-processingapparatus. In other words, in the case that the paper interval timebecomes shorter over the receiving condition of the post-processingapparatus, there is a possibility that the post-processing failure isgenerated.

Further, in Japanese Patent Application Laid-Open No. 2001-240285, thereis described that a speed of the inverting roller is adjusted in thecase of correcting the paper interval dispersion by the speed of theconveying unit. However, unless a speed of a downstream roller issimultaneously adjusted, there is generated a step out of a drivingmotor for the roller caused by tugging the sheet from both sides, adamage applied to the sheet caused by pressing the sheet based on aspeed difference between the inverting roller and the downstream roller.Further, since the sheet post-processing apparatus is not provided bytaking into consideration the paper interval time which can bepost-processed, for example, if the paper interval time becomes shorterthan the paper interval time which the sheet post-processing apparatuscan correspond to, there is a risk that the paper interval time can notbe corresponded by the sheet post-processing apparatus.

SUMMARY OF THE INVENTION

A technical feature of the present invention is made by taking thecircumstances mentioned above into consideration, and the presentinvention provides an image forming system which can detect a dispersionin a sheet conveyed within an image forming portion, and can stablycarry out an post-processing while securing a high image formingproductivity.

The image forming system according to the present invention has an imageforming portion which forms an image in a sheet, an inverting portionwhich inverts the sheet in which the image is formed by the imageforming portion, a discharging portion which discharges the sheetinverted by the inverting portion, a sheet position detecting portionwhich detects a position of the sheet in which the image is formed bythe image forming portion, a control portion which controls a motion ofthe inverting portion, and a sheet post-processing apparatus which isconnected to the image forming portion and receives the sheet dischargedfrom the discharging portion so as to apply an post-processing, whereinthe control portion can change the motion of the inverting portion basedon a detected information of the sheet position detecting portion, insuch a manner that an interval time of the continuous sheets becomesequal to or more than a sheet interval time which the sheetpost-processing apparatus can receive the sheet.

According to the present invention, it is possible to adjust the paperinterval time of the sheet discharged from the image forming portion ina range that the sheet post-processing apparatus can receive, whilesecuring a high image forming productivity.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view of a sheet conveying path of an imageforming system according to an embodiment of the present invention;

FIG. 2 is a sequence diagram at a time of conveying the sheet in theimage forming system in FIG. 1;

FIG. 3 is a block diagram of a control system of the image formingsystem in FIG. 1;

FIG. 4 is a flow chart describing a control of the image forming systemin FIG. 1; and

FIG. 5 is a flow chart describing another control of the image formingsystem in FIG. 1.

DESCRIPTION OF THE EMBODIMENTS

Embodiments according to the present invention will be described indetail below with reference to the accompanying drawings. In this case,dimensions, materials, shapes, relative arrangements and the like ofconstructing parts described in this embodiment are not in effect oflimiting the range of this invention to them, unless otherwisespecified.

First Embodiment

FIG. 1 is a view describing a sheet conveying path of one embodimentaccording to an image forming system of the present invention. FIG. 2 isa sequence diagram at a time of conveying the sheet in the image formingsystem in FIG. 1. FIG. 3 is a block diagram of a control system of theimage forming system in FIG. 1. FIG. 4 is a flow chart describing acontrol of the image forming system in FIG. 1.

In FIG. 1, an image forming system 1 has an image forming portion 10 anda finisher 100 corresponding to a sheet post-processing apparatus. Theimage forming portion 10 includes an image reader which reads a documentimage and is not illustrated and a printer. A document feeding apparatusis mounted to the image reader. The document feeding apparatus feeds thedocument which is set upward on a document tray, one by one from aleading page through a reading position on a platen glass via a curvedpath, and discharges to an external discharge tray.

In a sheet cassette 11, a sheet S is sequentially fed out by a sheetfeeding roller 12. The fed sheet S is conveyed to a registration roller16 which stops its rotating motion by path rollers 13 and 14. The sheetS conveyed to the registration roller 16 is removed its skew feeding. Inthe drawing, an image reference sensor 15 is arranged in a downstreamside of the path rollers 13 and 14, and serves as a sheet positiondetecting portion which detects a position of the fed sheet S.

A toner image formed on a photosensitive drum 21 is transferred to thesheet S in a transfer portion 20 in a state of aligning the toner imageformed on the photosensitive drum 21 with a position in a conveyingdirection of the sheet S conveyed from the registration roller 16, bydriving the registration roller 16 at a predetermined timing.

The transfer portion 20 is structured such that an endless transferringbelt 22 is wound around a drive roller 22 a and a driven roller 22 b,and a corona charger (not illustrated) for transferring is arranged inan approximately opposing portion of the photosensitive drum 21 in aninner side of the transferring belt 22.

Accordingly, it is possible to transfer and convey in a state that atransferring material is adsorbed to the transferring belt 22, and theimage transferred to the sheet S is fixed by a fixing portion 17. Inthis case, an extra toner and a paper powder on a surface of thetransferring belt 22 and a surface of the photosensitive drum 21 arecleaned.

The fixing portion 17 fixes a developer image on the sheet S bythermally pressing the sheet S. The sheet S passing through the fixingportion 17 is discharged toward a finisher 100 from a discharge port 27a corresponding to a discharge portion of the image forming portion 10via a switching member (a flapper) 18 and a discharge roller 27. Thedischarge port 20 a in this case is a portion serving as a sheetdelivery portion between the image forming portion 10 and the finisher100.

The sheet S conveyed by the discharge roller 27 and discharged from thedischarge port 27 a is received by a receiving roller 101 of thefinisher 100, and is discharged and stacked to a sheet stack tray 104 bya discharge roller 102 while directing the image forming surface upward.

In the case of discharging to the finisher 100 while directing the imageforming surface of the sheet S inversely, the sheet S discharged formthe fixing portion 17 is introduced to an inverting path in which afirst inverting roller 19 is arranged, by switching the switching member18.

In this case, a trailing end of the sheet S is conveyed to apredetermined amount downstream position of the fixing portion 17 whilebeing sped up, and a second inverting roller 24 is stopped in such amanner that the sheet trailing end is positioned at a predeterminedamount upstream position (an inverting point) of the second invertingroller 24, after being conveyed at the predetermined amount.

Thereafter, the sheet S is conveyed to the discharge roller 27 side byan inverting conveying roller 26 corresponding to a conveying portion byinverting the second inverting roller 24, and is conveyed to thefinisher 100. Further, in the drawing, a first inverting sensor 23 isarranged in an upstream side of the first inverting roller 19, anddetects a position of the sheet S before being inverted, and a secondinverting sensor 25 is arranged in a downstream side of the secondinverting roller 24, and detects a position of the sheet S after beinginverted.

The finisher 100 carries out each of processes such as a binding processand the like. The finisher 100 carries out a process of sequentiallyincorporating the sheet S discharged from the image forming portion 10,and aligning a plurality of incorporated sheets S so as to pack into onebundle, and a staple process of binding a trailing end of the packedsheet bundle by a staple 103.

Further, when the staple of the sheet bundle is selected from theoperation portion, the sheet bundle is bound by the staple 103 and isdischarged and stacked to the sheet stack tray 105, after finishing anpost-processing of aligning the trailing end and a width direction ofthe sheet S.

The first and second inverting rollers 19 and 24 are respectively drivenby first and second drivers 19 a and 24 a, as illustrated in FIG. 3.Further, the first and second drivers 19 a and 24 a are controlled by acontrol portion 30. The control portion 30 has a computing portion 31,and driving timings and sheet conveying speeds of the first and secondinverting rollers 19 and 24 are calculated based on detected informationof the first and second inverting sensors 23 and 25 and the imagereference sensor 15.

In this case, in FIG. 2, a nominal paper interval time of the imageforming portion 10 is set to A (ms) (refer to FIG. 4). Reference symbolA denotes a standard operate value calculated based on a productivity ofthe image forming system 1. Further, the paper interval time between apreceding sheet S1 and a subsequent sheet S2 in the image formingportion 10 including a feeding delay is set to ΔTp. The paper intervaltime ΔTp between the preceding sheet S1 and the subsequent sheet S2 inthe image forming portion 10 in this case is calculated based on aresult of detection of the preceding sheet S1 and the subsequent sheetS2 by the image reference sensor 15. The paper interval time between thepreceding sheet S1 and the subsequent sheet S2 which can be received bythe finisher 100 is set to be equal to or more than ΔTf. Further, thepaper interval time between the preceding sheet S1 and the subsequentsheet S2 in the inverting portion is set to ΔT.

If the paper interval time at a time of receiving the sheet becomes lessthan ΔTf, the post-processing such as the alignment of the subsequentsheet S2, the staple 103 and the like is too later, there is a risk thatthe post-processing failure is generated.

In order to prevent this, the computing portion 31 determines a timeΔTs1 until the second inverting sensor 25 detects the preceding sheet S1after the image reference sensor 15 detects the preceding sheet S1. Thecomputing portion 31 determines a time ΔTs2 until the second invertingsensor 25 detects the subsequent sheet S2 after the image referencesensor 15 detects the subsequent sheet S2. Further, the computingportion 31 calculates a value obtained by adding the paper interval timeΔTp between the preceding sheet S1 and the subsequent sheet S2 which aredetected by the image reference sensor 15, to a difference between ΔTs1and ΔTs2, as the paper interval time ΔT between the preceding sheet S1and the subsequent sheet S2 in the inverting portion.

As illustrated in a flowchart in FIG. 4, the control portion 30transmits a signal to the first and second drivers 19 a and 24 a in sucha manner that a paper interval time (a sheet interval time between thepreceding sheet and the subsequent sheet in the discharge port 27 a) ata time of discharging the sheet S becomes equal to or more than ΔTf incorrespondence to the calculated ΔT. Accordingly, the first and secondinverting rollers 19 and 24 are controlled by the control portion 30,and adjust a start timing and an inverting speed of the sheet S from theinverting point. The inverting speed in this case means a conveyingspeed of the sheet by the second inverting roller 24 after beinginverted or a conveying speed of the sheet by the inverting conveyingroller 26 provided in the downstream side of the second inverting roller24.

For example, the conveying speed of the preceding sheet S1 is sloweddown due to an influence of the fixing portion 17 and a slip and anabrasion of the first and second inverting rollers 19 and 24. There isconsidered a case that it is delayed to reach the inverting point andthe subsequent sheet S2 is conveyed faster than a target conveying speedunder the transient influence of the fixing portion 17 without beingaffected by a reduction of a conveying efficiency (refer to a dottedportion in FIG. 2).

In this case, a start timing of the inverting portion of the subsequentsheet S2 is delayed. In other words, the start timing at the invertingpoint is set to be equal to or more than a paper interval time ΔTf whichis a limit of receiving the finisher 100 and equal to or less than apaper interval time ΔTp at which a productivity of the image formingsystem 1 does not degrade. The start timing of the inverting portionmeans a timing for inverting the second inverting roller 24 afterstopping the second inverting roller 24 in a state that the sheet rearand is positioned at a predetermined position in an upstream side of thesecond inverting roller 24.

With such a state, for example, in the case that a time for which thethird sheet S3 reaches the inverting point is longest in the dispersion(the third sheet S3 is delayed), the inversion is started by quickeningthe start timing of the inverting portion while targeting at a pointnear ΔTf. Otherwise, in the case that the time for which the sheet S3reaches the inverting point is shortest in the dispersion (the sheet S3reaches earlier), the start timing of the inverting portion is delayedwhile targeting at ΔTp.

In other words, the paper interval time A of the image forming portion10 is compared with ΔTp (step 1), and in the case that ΔTp is largerthan the paper interval time A due to the feeding delay in the upstreamside than the image forming portion, the inversion is carried outaccording to a normal control (step 2). In the case that ΔTp is equal toor less than the paper interval time A, ΔT is compared with ΔTp (step3), and if the paper interval time ΔT at the inverting point becomesequal to or more than ΔTp, the start timing of the first and secondinverting rollers 19 and 24 is quickened at the difference (step 4).

Accordingly, it is possible to prevent the paper interval time ΔT frombecoming short at the inverting point of the subsequent sheet S2. In thecase that the paper interval time ΔT at the inverting point becomesshorter than ΔTp, ΔT is compared with the paper interval time ΔTf of thereceiving condition of the finisher 100 (step 5), and if ΔT is equal toor more than ΔTf, the inversion is carried out as it is in accordancewith the normal control (step 6). In the case that ΔT is smaller thanΔTf, the start timing of the inverting roller (the timing at which thesecond inverting roller 24 is inverted) is delayed only at thedifference between ΔTf and ΔT, in such a manner that the paper intervalbecomes equal to or more than the paper interval time ΔTf which can bereceived by the finisher 100 (step 7).

As mentioned above, even in the case that the paper interval dispersionis generated within the image forming portion 10, it is possible tomaintain a stable conveying performance without degrading theproductivity of the image forming system 1, while satisfying thereceiving condition of the finisher 100.

Second Embodiment

In a second embodiment according to the present invention, in the caseof discharging the sheet S to the finisher 100 while inverting the imageforming surface of the sheet S after forming the image by the imageforming portion 10, the sheet S is sped up in a convey region by theinverting conveying roller 26.

Further, the sheet leading end is slowed down to a speed which canreceived the finisher 100 at a predetermined amount upstream position ofthe discharge roller 27, and the sheet is discharged from the dischargeport 27 a by the discharge roller 27. In this case, the computingportion 31 calculates ΔT obtained by adding ΔTp to the differencebetween ΔTs2 and ΔTs1. A sheet conveying speed or a speed change timingby the inverting conveying roller 26 is controlled in such a manner thatthe paper interval becomes equal to or more than ΔTf corresponding tothe receiving condition of the finisher 100 and becomes equal to or lessthan ΔTp at which the productivity of the image forming system 1 doesnot degrade.

These controls will be specifically described with reference to FIG. 5.First, ΔTp is compared with the paper interval time A of the imageforming portion 10 (step 1), and in the case that ΔTp is larger than Adue to the feeding delay, the inversion is carried out in accordancewith a normal control (step 2).

In the case that ΔTp is equal to or less than the paper interval time A,ΔTp is compared with the paper interval time ΔT at the inverting point(step 3), and if ΔT is equal to or more than ΔTp, a distance at whichthe speeding up is carried out in an inverting path is made longer atthe difference, and a position starting the slowing down is set to adownstream side (step 4).

Accordingly, it is possible to prevent the paper interval time ΔT frombecoming short at the inverting point of the subsequent sheet S2. In thecase that the paper interval time ΔT at the inverting point becomesshorter than ΔTp, ΔT is compared with ΔTf (step 5), and it is determinedwhether or not ΔT is equal to or more than the paper interval time ΔTfof the receiving condition of the finisher 100.

If ΔT is equal to or more than ΔTf, the inversion is carried out as itis in accordance with the normal control (step 6). In the case that ΔTis smaller than ΔTf, the distance is made shorter by carrying out thespeed-up conveying in the inverting path at the difference between ΔTfand ΔT in such a manner that the paper interval becomes equal to or morethan ΔTf, and the position starting slowing down is set to an upstreamside (step 7).

As mentioned above, it is possible to maintain the stable conveyingperformance without degrading the productivity of the image formingsystem 1 by controlling in such a manner as to adjust the slowing downpoint.

In this case, as the first embodiment, the embodiment that the paperinterval is adjusted in such a manner as to be received by the finisher100 by controlling the start timings of the first and second invertingrollers 19 and 24 is described. Further, as the second embodiment, theembodiment that the paper interval is adjusted in such a manner that thefinisher 100 can receive by controlling the speed of the invertingconveying roller 26 is described. However, the structure may be madesuch as to adjust so as to achieve such a paper interval that thefinisher 100 can receive by controlling both the start timings of thefirst and second inverting rollers 19 and 24 and the speed of theinverting conveying roller 26.

Third Embodiment

In a third embodiment according to the present invention, the imageforming portion 10 to which a plurality of finishers 100 can beconnected receives the information of the receiving time set in each ofthe finishers 100 by the image forming portion 10 side. It is possibleto control the inverting timings of the first and second invertingrollers 19 and 24 and the conveying speed of the inverting conveyingroller 26 such as to discharge at a paper interval time which is equalto or more than a lower limit value of the receiving time of thefinisher 100 and equal to or more than such a paper interval time as toprevent the productivity from degrading based on the information.

As mentioned above, the information of the receiving paper interval timeis received in the image forming portion 10 side from the finisher 100,and the paper interval time of the discharge is controlled incorrespondence to the finisher 100. Accordingly, it is possible toobtain the image forming system 1 which can maintain the stableconveying performance in correspondence to the various accessorieswithout degrading the productivity.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2007-296383, filed Nov. 15, 2007, which is hereby incorporated byreference herein in its entirety.

1. An image forming system comprising: an image forming portion whichforms an image in a sheet; an inverting portion which inverts the sheetin which the image is formed by the image forming portion; a dischargingportion which discharges the sheet inverted by the inverting portion; asheet position detecting portion which detects a position of the sheetin which the image is formed by the image forming portion; a controlportion which controls a motion of the inverting portion; and a sheetpost-processing apparatus which is connected to the image formingportion and receives the sheet discharged from the discharging portionso as to apply an post-processing, wherein the control portion canchange the motion of the inverting portion based on a detectedinformation of the sheet position detecting portion, in such a mannerthat an interval time of the continuous sheets becomes equal to or morethan a sheet interval time which the sheet post-processing apparatus canreceive the sheet.
 2. The image forming system according to claim 1,wherein the inverting portion includes a rotating body rotating andconveying the sheet in which the image is formed by the image formingportion, in one direction and thereafter rotating and conveying in aninverting direction, and the control portion is capable of changing arotation start timing of the roller in the other direction based on thedetected information of the sheet position detecting portion, in such amanner that an interval between the continuous sheets becomes equal toor more than a sheet interval time which the sheet post-processingapparatus is capable of receiving.
 3. The image forming system accordingto claim 2, wherein the control portion delays the rotation start timingof the roller in the other direction at a time of conveying a subsequentsheet, in the case that an interval time between continuous precedingsheet and subsequent sheet detected by the sheet position detectingportion is shorter than a predetermined time.
 4. The image formingsystem according to claim 1, wherein the inverting portion conveys thesheet in one direction, temporarily stops the sheet and thereafterconveys the sheet in the other direction, the inverting portion startsconveying the sheet in the other direction and thereafter conveys thesheet to the discharging portion in a state of slowing down to apredetermined speed, and the control portion is capable of changing atiming for slowing down the conveying speed of the sheet based on thedetected information of the sheet position detecting portion after theinverting portion conveys the sheet in the other direction in such amanner that an interval time of the continuous sheets becomes equal toor more than a sheet interval time which the sheet post-processingapparatus is capable of receiving.
 5. The image forming system accordingto claim 4, wherein the control portion sets a position starting slowingdown a subsequent sheet after the inverting portion conveys thesubsequent sheet in the other direction to an upstream side, in the casethat the interval time between the continuous preceding sheet andsubsequent sheet detected by the sheet position detecting portion isshorter than a predetermined time.
 6. The image forming system accordingto claim 1, wherein the control portion is capable of changing aconveying speed of the inverting portion based on the detectedinformation of the sheet position detecting portion in such a mannerthat an interval time of the continuous sheets at a time of beingdischarged from the discharging portion becomes equal to or more than asheet interval time which the sheet post-processing apparatus is capableof receiving.
 7. The image forming system according to claim 1, whereinthe inverting portion includes a rotating body rotating and conveyingthe sheet in which the image is formed by the image forming portion inone direction and thereafter rotating and conveying in an invertingdirection, and the control portion controls a rotation start timing ofthe roller in the other direction and a sheet conveying speed by theroller based on the detected information from the sheet positiondetecting portion.
 8. The image forming system according to claim 1,wherein the control portion changes a motion of the inverting portion insuch a manner as to achieve a paper interval time at which the sheetpost-processing apparatus is capable of receiving, in the case that theinterval time of the sheet detected by the sheet position detectingportion is shorter than a predetermined time.